The present invention relates to a flow soldering process for mounting a component(s) such as an electronic component(s) onto a board (or substrate) by means of a solder material, and also relates to an apparatus for such process.
A flow soldering process utilizing a molten solder material in the form of a wave(s) has been conventionally known as one of processes for connecting an electronic component or the like to a board in the field of production of an electronic circuit board. Such flow soldering process generally includes a flux applying step for applying flux onto a board, a preheating step for heating the board in advance, and a solder material supplying step for supplying a solder material to the board by contacting the board with a wave(s) of the solder material. Hereinafter, the conventional flow soldering process will be described with reference to the drawings. FIG. 15 is a schematic side view of the conventional flow soldering apparatus while showing its internal construction. FIG. 16 is a schematic view of the flow soldering apparatus of FIG. 15 when viewing it from a cross section taken along an Xxe2x80x2xe2x80x94Xxe2x80x2 line.
At first, a board is supplied with flux by a flux supplying means (not shown) while applying the flux onto a lower surface of the board. The board is, for example, a printed circuit board onto which an electronic component such as a xe2x80x9cthrough hole insertion component (or an inserted component)xe2x80x9d (i.e. a component a part of which is inserted into a through hole, for example, a discrete component or a lead component) is to be mounted at a predetermined position according to a known manner. The flux generally contains an active ingredient such as rosin (a resin component) as well as a solvent such as isopropyl alcohol. The flux applying step for applying such flux to the board is conducted in order to improve wettability and a spreading property of the solder material on a surface of a land formed on or through the board (i.e. a portion to be supplied with the solder material) by removing an oxide film (a naturally oxidized film) which is unavoidably formed on the land. As the flux supplying means (or device), a spray fluxer for spraying the flux in the form of mist to the board, a foam fluxer for contacting the board with the flux in the form of foam or the like can be used. These flux supplying means can be situated separately from a flow soldering apparatus 60 of FIG. 15, though the flux supplying means can form the flow soldering apparatus 60 by integrally incorporating the flux supplying means in the flow soldering apparatus 60.
The board 71 applied with the flux as described above is then fed into the flow soldering apparatus 60 shown in FIG. 15 through an inlet 61 thereof. The board 71 is mechanically conveyed in a direction of an arrow 62 (hereinafter referred to as a conveyance direction) inside the apparatus 60 (along the conveyance line shown as a broken line in FIG. 15) at a substantially constant speed. More specifically, the conveyance of the board 71 is conducted by holding the board 71 with conveyance fingers 72a and 72b at its both edge portions which locate on opposed right and left sides of the board when viewing the board towards the conveyance direction 62 as shown in FIG. 16 and by mechanically moving the conveyance fingers 72a and 72b in the conveyance direction of the arrow 62. The conveyance fingers 72a and 72b are connected to chains 74a and 74b respectively and run around conveyer frames 73a and 73b respectively in a plane parallel to a principal plane of the board 71. The conveyer frames 73a and 73b extend from the inlet 61 to an outlet 69 shown in FIG. 15. The conveyer frame 73a is a base conveyer frame which is fixed, and the conveyer frame 73b is a width adjustable conveyer frame which can slide in directions being perpendicular to the conveyance direction and able to keep parallel to the fixed conveyer frame 73a (in other words, which directions are shown as a left and right arrow in FIG. 16 and lateral in the sheet of FIG. 16).
The board 71 conveyed in the apparatus 60 from the inlet 61 toward the outlet 69 as described above is firstly heated by a preheater 63 locating under the conveyance line of the board, for example a far infrared heater. Such heating step is referred to as a preheating step. The preheating step is conducted for vaporizing and removing an unnecessary solvent ingredient in the flux applied onto the board 71 through the above described flux applying step so as to leave only the active ingredient on the board 71 and also for preheating the board 71 prior to supply of a solder material 64 to the board 71 so as to alleviate a heat shock of the board 71 upon contacting the board 71 with a molten solder material 64. The preheater 63 is located under the conveyance line by generally being put on a bottom of a channel structure (or support) 76 which is open on its upside and which is connected to the fixed conveyer frame 73a and a fixed frame 75 at its top portions. Thus, the preheater 63 heats the board 71 from a lower side of the board 71 which is the same side to which the solder material is supplied in the following solder material supplying step.
The board 71 is subsequently conveyed above a solder material supplying means (or unit) 66 which includes a solder bath 65. The solder bath 65 contains the solder material 64 which is in a molten state by heating beforehand. A distance xe2x80x9cd1xe2x80x9d between the preheater 63 and the solder bath 65 (i.e. a distance along the conveyance direction between them) is generally about 70 to 150 mm. When the board 71 goes over the solder material supplying means 66, the board 71 is contacted at the lower surface of the board 71 with a primary wave 67 and a secondary wave 68 of the solder material 64, so that the solder material 64 is supplied to the board 71. As the solder waves 67 and 68 are shown in FIG. 17 while enlarging them, a distance xe2x80x9cd2xe2x80x9d between the primary wave 67 and the secondary wave 68 (more specifically, a distance along the conveyance direction from a position at which a certain point of the board 71 leaves the primary wave to a position at which the certain point begins to contact with the secondary wave) is generally about 80 to 150 mm.
In this solder material supplying step, the solder material 64 which is supplied in the form of the primary wave 67 rises in an annular space between a land portion and a lead 74 of the through hole insertion component 73 from a lower side of the board 71 by the capillary phenomenon as shown in FIG. 18, wherein the land portion forms a wall of the through hole 72 perforated through the board 71 and the lead has been inserted through the through hole from an upper side of the board. An excess amount of the solder material 64 adhering to the lower surface to the board 71 by the primary wave is removed by subsequently contacting the solder material 64 in the form of the secondary wave 68 with the board 71. Then, the solder material which is supplied and adheres to the board 71 solidifies with a drop in its temperature and forms a so-called xe2x80x9cfilletxe2x80x9d as a connection portion of the solder material.
In such solder material supplying step (or flow soldering step), the primary wave 67 is directed for sufficiently wetting a surface of the land 75 which covers the wall of the through hole 72 (as well as wetting the lead 74 of the electronic component) with the solder material and for supplying the solder material into the through hole 72. If it is insufficient, the solder material does not rise up along the annular space between the lead 74 and the land portion which forms the wall of the through hole 72, so that there occurs a problem of a so-called xe2x80x9cred eye (or non-wetting)xe2x80x9d (which is referred to as xe2x80x9cakamexe2x80x9d in Japanese), for example. The xe2x80x9cred eyexe2x80x9d is, in other words, a phenomenon in which the land which is generally made of copper shows its color and the land is observed like as a red colored eye since an annular land portion locating on the upper surface of the board is not covered with the solder material but exposed, and the xe2x80x9cred eyexe2x80x9d may also be referred to as an xe2x80x9cinsufficient rising (or insufficient wetting up)xe2x80x9d (shortage of the supply of the solder material to the through hole resulting from insufficient rising of the solder material by the capillary action). On the other hand, the secondary wave 68 is directed for removing an excess amount of the solder material which is adhering to an area of the lower surface of the board covered with a solder resist and also for conditioning the fillet form. If the removing and conditioning is unsatisfactory, the solder material remains on an area between lands and solidifies thereon to undesirably form a so-called xe2x80x9cbridgexe2x80x9d (such bridge is undesirable since it causes a short circuit) or a ceratoid projection.
The lead of the electronic component is electrically and physically connected to the land of the board by the fillet of the solder material as described above. The resultant board 71 is thereafter taken out through the outlet 69 (see, FIG. 15). Thus, an electronic circuit board is produced wherein the electronic component has been soldered to the board according to the flow soldering process.
For the electronic circuit board produced as described above, an Snxe2x80x94Pb based solder material which contains Sn and Pb as main constituents (or components), especially an Snxe2x80x94Pb eutectic solder material is commonly used. However, lead contained in such an Snxe2x80x94Pb based solder material may cause environmental pollution if it is subjected to an inadequate waste treatment, so that a solder material containing no lead, i.e. a so-called lead-free solder material, has started to be used as an alternative of the solder material containing lead in an industrial scale.
However, when the flow soldering is conducted by utilizing the conventional process and apparatus just while substituting the lead-free solder material for the Snxe2x80x94Pb based material, there arise a problem that an occurrence ratio of the so-called xe2x80x9cred eyexe2x80x9d (or xe2x80x9cinsufficient risingxe2x80x9d) or xe2x80x9cbridgexe2x80x9d is increased compared with using the Snxe2x80x94Pb based material. Therefore, it is not necessarily appropriate in the case of using the lead-free solder material to utilize the conventional flow soldering process and apparatus just as they are.
The present invention is directed to solve the prior art problems as described above. The present invention aims to provide a flow soldering process for mounting an electronic component onto a board with a solder material, which is appropriate to a case of using a lead-free solder material as the solder material, and can alleviate and preferably solve at least a part of the problems as described above. The present invention also aims to provide an apparatus for performing such flow soldering process.
The inventors have found that one cause for the above problems resides in a higher melting point of the lead-free solder material compared with that of the Snxe2x80x94Pb based material. Further, we also found that though the lead-free solder material generally has a higher melting point than that of the Snxe2x80x94Pb based material, an operation temperature of the flow soldering using the lead-free solder material is not increased compared with an operation temperature of the conventional flow soldering using the Snxe2x80x94Pb solder material by a certain extent which corresponds to the difference between the melting points of the lead-free solder material and the Snxe2x80x94Pb based solder material.
As to the melting points of the general lead-free solder material, it is about 220xc2x0 C. for an Snxe2x80x94Agxe2x80x94Cu based material, and about 227xc2x0 C. for an Snxe2x80x94Cu based material. These melting points are higher than that of the Snxe2x80x94Pb eutectic solder material of 183xc2x0 C. by about 30 to 50xc2x0 C. On the other hand, the operation temperature of the flow soldering process using the lead-free solder material is about 250 to 255xc2x0 C., and increased by only about 10 to 15xc2x0 C. from the conventional operation temperature for the Snxe2x80x94Pb based solder material of about 235 to 245xc2x0 C. (The operation temperature as one measure in the present specification is a liquid temperature of the molten solder material in the solder bath.)
It can be considered that wettability of a molten metal material generally depends on a temperature difference on a basis of a melting temperature of the metal material (in other words, a temperature difference obtained by subtracting the melting temperature of the metal material from an actual temperature of the metal material in the molten state), and the wettability becomes lower as the temperature difference becomes smaller. Based on this consideration, the wettability of the lead-free solder material is seems to be lower than the wettability of the Snxe2x80x94Pb solder material since the temperature difference by subtracting the melting temperature from the operation temperature in the case of using the lead-free solder material is smaller than when using the Snxe2x80x94Pb based material.
By the way, the actual temperature of the solder material varies depending on the situation in which the solder material is located, and the actual temperature is highest when the solder material is in the molten state in the solder bath and thereafter decreases by contacting the solder material in the form of a solder wave with the board having a lower temperature thereby losing an amount of heat of the solder material through the board. Though the temperature decrease in the case of using the Snxe2x80x94Pb based solder material would be to such an extent that a problem is not caused, the temperature decrease in the case of using the lead-free solder material will remarkably influence its wettability thereby to inhibit the molten lead-free solder material supplied by the form of the primary wave from sufficiently rising in an annular space between a lead and a land portion which forms a wall of a through hole and therefore causing the so-called xe2x80x9cred eyexe2x80x9d.
Further in the case of using the lead-free solder material, it can be considered that the molten solder material supplied by the primary wave and adhering to the board loses an amount of its heat through the board and/or an ambient atmosphere before the board make contact with a fresh solder material by the secondary wave, and therefore decreases its temperature to partially solidify. Such a temperature decrease in the case of using the Snxe2x80x94Pb based solder material does not cause a problem. In the case of using the lead-free solder material, however, the solder material will be sensitively influenced by a small temperature decrease during a period after leaving the primary wave of the board before contacting with the secondary wave, so that the solder material starts to solidify during this period. Since solder material has solidified during the period after leaving the primary wave before contacting with the secondary wave (in other words, while a certain point of the board passes through a distance xe2x80x9cd2xe2x80x9d shown in FIG. 17), the solidified solder must be melted again by the secondary wave. If the solder material is not sufficiently melted by the secondary wave, this may causes a so-called xe2x80x9cbridgexe2x80x9d to be formed.
As described above, one cause of the problems of the xe2x80x9cbridgexe2x80x9d, the xe2x80x9cinsufficient risingxe2x80x9d and so on which may occur in the flow soldering process using the lead-free solder material resides the fact that the solder material supplied to the board decreases its temperature excessively relative to its high melting point by losing an amount of its heat through the board during the flow soldering process, especially in a solder material supplying step.
In order to eliminate such cause and avoid the occurrence of the xe2x80x9cinsufficient risingxe2x80x9d, the xe2x80x9cbridgexe2x80x9d and so on of the solder material resulting from the temperature decrease of the solder material upon soldering, it might be suggested to further increase the operation temperature of soldering in the case of using the lead-free solder material so as to make a temperature difference between the operation temperature and the melting temperature of the solder material similar to that in the conventional case which uses the Snxe2x80x94Pb based solder material. However, it is impossible to further increase the operation temperature while using the conventional apparatus because of constraint of heat resistance as to the board, the components and so on.
Therefore, for the purpose of decreasing an occurrence ratio of the xe2x80x9cinsufficient risingxe2x80x9d, the xe2x80x9cbridgexe2x80x9d and so on, we have further studied suppressing the temperature decrease of the solder material in the solder material supplying step of the flow soldering process.
The temperature decrease of the solder material, as described above, seems to be caused by losing an amount of heat from the solder material (more specifically, the solder material supplied by the form of the primary wave) through the board and the ambient atmosphere surrounding the board. Thus, we have conceived that the occurrence ratio of the xe2x80x9cinsufficient risingxe2x80x9d, the xe2x80x9cbridgexe2x80x9d and so on which may be caused in the flow soldering using the lead-free solder material can be lowered, for example, by improving thermal efficiency in a preheating step before the solder material is supplied to the board so as to maintain a temperature of the board itself higher (or to suppress the temperature decrease of the board), or by suppressing the temperature decrease of the solder material which has been supplied to the board by the form of the primary wave.
On the basis of such knowledge, we have developed a flow soldering process improved by various approaches as well as an apparatus for such flow soldering process.
It is noted that the temperature of a board means a temperature of a lower surface of the board, more specifically a temperature of a land portion located on the lower surface (or a back side) of the board. Such temperature can be measured by, for example, contacting a thermocouple with the land portion located on the lower surface of the board (for example by bonding it to the land portion) and recording data obtained from the thermocouple. Thus, the temperature decrease of the board can be calculated based on the obtained data.
More specifically, there are provided various flow soldering processes and apparatuses as described below based on the present invention. According to those flow soldering processes and/or apparatus, the occurrence ratio of the xe2x80x9cinsufficient risingxe2x80x9d, the xe2x80x9cbridgexe2x80x9d and so on upon the flow soldering can be maintained at an extent which is not larger than that in the conventional case of using the Snxe2x80x94Pb based solder material.
In one aspect of the present invention, there is provided a flow soldering process for mounting an electronic component onto a board by means of a solder material, which process includes: a preheating step for previously heating the board, which is provided with the electronic component and conveyed, by using a preheater locating under the board and a heating cover extending over the board; and a solder material supplying step for supplying the solder material in a molten state to the board by contacting the solder material as a primary wave and a successive secondary wave with a lower surface of the board. It is noted that a device (or heater) is herein referred to as the preheater, which device previously heats the board prior to the solder material supplying step by heating the board from its lower side while locating under the board as in the conventional apparatus.
In another aspect of the present invention, there is provided a flow soldering apparatus for mounting an electronic component onto a board by means of a solder material, which apparatus includes: a preheater locating under the board which is provided with the electronic component and conveyed; a heating cover locating above the preheater so as to extend over (or cover the above of) the board; and a solder material supplying means (or unit or device) for supplying the solder material in a molten state to the board by contacting the solder material as a primary wave and a successive secondary wave with a lower surface of the board, the means locating downstream of the preheater in a direction of conveyance of the board.
In the preheating step prior to the solder material supplying step in the conventional process as shown in FIGS. 15 and 16, heating of the board 71 by the preheater 63 such as a far infrared heater locating under the conveyance line of the board 71 was conducted in such a condition that a preheating zone which is a part of a conveyance space (that is, a space through which the board 71 is conveyed) and which locates above the preheater 63 (wherein such preheating zone is also a space inside the channel structure 76 (see, FIG. 16)) is not substantially isolated form a space outside the channel structure 76 and communicated with this space through an opening at a top of the channel structure 76. The board 71 is exposed to a preheating atmosphere gas which is formed by heating an atmosphere gas in the preheating zone by the preheater 63. In this process, however, an amount of heat of the preheating atmosphere gas escapes and scatters into an ambient gas outside the channel structure 76 having a temperature lower than that of the preheating atmosphere gas.
According to the process or an apparatus of the present invention, on the other hand, the preheater locating under the board (or the conveyance space or the conveyance line of the board) and the heating cover extending over the board (or closing a top of the conveyance space or above the conveyance line of the board) are used, so that the preheating atmosphere gas in the preheating zone between the preheater and the heating cover is isolated from the ambient gas outside the preheating zone having the lower temperature to suppress heat dissipation of the preheating atmosphere gas, which results in improved thermal efficiency. Thus, the board can be heated to a higher temperature because of the higher thermal efficiency according to the process or the apparatus of the present invention described above even when an amount of heat supply is equal to that in the conventional process.
Furthermore, the xe2x80x9cheating coverxe2x80x9d used for the process or the apparatus of the present invention as described above has a function of heat generation for heating in addition to the function as the cover for isolating the preheating atmosphere gas to some extent as described above. Therefore, it is possible to heat the board not only from its lower side by means of the preheater but also from its upper side by means of the heating cover (or a heat generation cover) having the function to emit heat. Thus, the board can be heated to a temperature further higher than that in the conventional process using only the preheater.
As a results of these, it is possible to heat the board in the preheating step to the temperature higher than in the conventional case and in turn to transfer the board having the higher temperature to the following solder material supplying step, and therefore to keep a temperature of the board higher at the beginning of the solder material supplying step.
It is noted that the heating cover described above preferably rises the temperature of the board positively, but it may generate a heat to such an extent that decrease in the temperature of the board can be prevented compared with a case without the heating cover. In the heating cover, a heat generation body having the function to emit heat (or a heater) and a cover body may not be integral to form a single body. Preferably, the heating cover described above (more specifically the heat generation body which constitutes the heating cover) is composed of plural sections (which are preferably located along the conveyance direction), and heating of each section as to heating using such heating cover is controlled.
In a preferred embodiment, the heating cover described above extends not only above the preheater but also above the solder material supplying means so as to cover the board. As shown in FIG. 15, a solder material supplying zone which is a part of the conveyance space for the board 71 and located above the solder material supplying unit 66 (more specifically, above the solder material 64 in the solder bath 65) is not covered by a cover and is communicated with its surrounding space, so that a heat radiated from the molten solder material and so on escapes and scatters into an atmosphere gas in the surrounding space having a lower temperature. On the other hand, since the heating cover extending over both of the preheater and the solder material supplying unit is provided as in this preferred embodiment of the present invention, not only the preheating atmosphere gas in the preheating zone but also the atmosphere gas in the solder material supplying zone between the heating cover and the solder material supplying unit (more specifically, the solder material in the solder bath) can be isolated from the atmosphere gas surrounding them and having the lower temperature. Thus, the heat dissipation from the solder material supplying zone can be suppressed and therefore the thermal efficiency can be further improved. Thus, the temperature of the board can be kept higher. In this embodiment, the heating cover preferably heats the board in the solder material supplying step (or in the solder material supplying zone) in addition to the preheating step (or in the preheating zone), wherein the phrase xe2x80x9cheats the boardxe2x80x9d includes prevention of the temperature decrease of the board.
In a preferred embodiment, an apparatus of the present invention further includes a forced convection generating means (or device) for forcedly convecting (or mixing) the preheating atmosphere gas in the preheating zone between the heating cover and the preheater. According to this embodiment of the present invention, since the preheating atmosphere gas heated by the preheater and the heating cover is forcedly convected in the preheating zone, a temperature of the preheating atmosphere gas can be made uniformly, and the thermal efficiency of the preheating zone as a whole can be further improved, and the temperature of the board can be made further higher.
As the forced convection generating means, for example, a fan or a gas blowing means (or device) can be used. The fan can circulate the preheating atmosphere gas in the preheating zone. As the gas blowing means, a compressor can be used which blows a gas such as an air and preferably nitrogen gas having a temperature of, for example, about 200 to 400xc2x0 C. and supplies it into the preheating zone. When the gas blowing means is used, it is preferable to supply the gas (e.g. gas having a temperature higher than that of the atmosphere gas in the preheating zone) into the preheating zone while suctioning the atmosphere gas in the preheating zone.
According to another aspect of the present invention, there is provided a flow soldering process for mounting an electronic component onto a board by means of a solder material, which process includes: a preheating step for previously heating the board, which is provided with the electronic component and conveyed, by using a preheater locating under the board; and a solder material supplying step for supplying the solder material in its molten state to the board by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board which has been previously heated, wherein a temperature decrease of the board during a period after having previously been heated in the preheating step before contacting with the primary wave is not larger than 3xc2x0 C.
The temperature decrease of the board after during a period after the board has been heated by the preheater (and a heating cover as described above in case) in the preheating step (that is, after the board has passed a position which is just above a downstream end of the preheater) and before the board comes in contact with the primary wave by the solder material supplying means in the solder material supplying step is generally not greater than about 3xc2x0 C. and preferably not greater than about 2xc2x0 C. according to a process of the present invention described above, though it is about 5 to 20xc2x0 C. in the conventional process. Since the temperature decrease of the board until the board contacts with the primary wave is made smaller, the temperature of the board at the beginning of the solder material supplying step becomes higher.
More concretely, the temperature decrease of the board can be made 3xc2x0 C. or smaller by setting a gap at 20 to 60 mm between the preheater for previously heating the board (more specifically, the downstream end of the preheater) and a solder bath which contains the solder material in the molten state and forms the primary wave and the secondary wave which contact with the lower surface of the board (more specifically, an upstream end of the solder bath).
Thus, according to other aspect of the present invention, there is provided a flow soldering apparatus for mounting an electronic component onto a board by means of a solder material, which apparatus includes: a preheater locating under the board which is provided with the electronic component and conveyed; and a solder material supplying means for supplying the solder material in its molten state contained in a solder bath to the board by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board, wherein the unit locating downstream from the preheater in a direction of conveyance of the board is constructed to have a gap between the preheater and the solder bath within 20 to 60 mm.
The gap between the preheater and the solder bath is conventionally about 100 mm or more. Since the gap in an apparatus of the present invention is made narrower than that in the conventional apparatus, a time required for the board to pass the gap is shortened, and the temperature decrease of the board is lowered when it is conveyed above the gap, and therefore the temperature of the board at the beginning of the solder material supplying step can be made higher. It is noted that the gap having a width of at least about 20 mm is required to prevent an accident of a short circuit in the preheater.
In a preferred embodiment, the apparatus of the present invention described above is provided with a closing means (or device or element) for closing the gap between the preheater and the solder bath to obstruct a stream of an atmosphere gas passing through the gap.
In the conventional apparatus, since there is generally a gap between the preheater and the solder bath in order to prevent an accident of a short circuit as described above while sucking an atmosphere gas in a space through which the board was conveyed and passed (also, referred to as a xe2x80x9cconveyance spacexe2x80x9d) into an exhaust duct locating above the board so as to discharge it out in order to remove smoke outside which generates upon vaporization of the flux, an atmosphere gas having a temperature lower than that of the atmosphere gas in the conveyance space of the board flows into through the gap between the preheater and the solder bath upwardly from downside of the gap and entered into the conveyance space locating above the gap from outside of the conveyance space. As a result, a temperature of the board was directly decreased by contacting the atmosphere gas having the lower temperature with the board to carry an amount of heat away from the board, or indirectly decreased by carrying away an amount of heat away from the atmosphere gas in the preheating zone and/or in the solder material supplying zone, in which the preheating zone and the solder material supplying zone are located upstream and downstream of the gap, respectively. However, according to this embodiment of the present invention, since a stream of such atmosphere gas having the lower temperature is obstructed by the closing means (or closure) for closing the gap, the temperature decrease of the board during passing of the board through a space above the gap is further reduced and the temperature of the board at the beginning of the solder material supplying step can be made higher.
In yet another aspect of the present invention, there is provided a flow soldering process for mounting an electronic component onto a board by means of a solder material, which process includes: a preheating step for previously heating the board, which is provided with the electronic component and conveyed, by using a preheater locating under the board; and a solder material supplying step for supplying the solder material in its molten state to the board by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board, while an atmosphere gas in a space above the solder material in the molten state is thermally isolated from a gas which is downstream from the atmosphere gas in a direction of conveyance of the board and has a temperature lower than that of the atmosphere gas.
In yet another aspect of the present invention, there is provided a flow soldering apparatus for mounting an electronic component onto a board by means of a solder material, which apparatus includes: a preheater locating under the board which is provided with the electronic component and conveyed; a solder material supplying unit for supplying the solder material in its molten state to the board by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board, the unit locating downstream from the preheater in a direction of conveyance of the board; and an isolation means (or device) for thermally isolating an atmosphere gas in a space above the solder material supplying unit from a gas which is present downstream of the atmosphere gas in a direction of conveyance of the board and has a temperature lower than that of the atmosphere gas.
Generally, an atmosphere gas in the solder material supplying zone is heated by the solder material used in the solder material supplying step and having a high temperature (as well as by the preheater used in the preheating step) to a high temperature. According to the process or the apparatus of the present invention as described above, since such an atmosphere gas in the solder material supplying zone having a relatively high temperature is thermally isolated from an atmosphere gas which locates downstream of the solder material supplying zone in a direction of the conveyance of the board and which has a temperature lower than that of the atmosphere gas in the solder material supplying zone, dissipation of heat of the atmosphere gas in the solder material supplying zone is effectively alleviated. Thus, in the solder material supplying step, the board can be exposed to an atmosphere gas having a higher temperature, and a temperature of the board can be made higher.
In a preferred embodiment, the isolation means as described above is an air curtain or a mechanical shutter.
The air curtain is formed by flowing a gas (preferably a gas having a high temperature) across the conveyance space (or the conveyance line) of the board. Though air, nitrogen gas or the like can be used as such gas, the nitrogen gas is preferable. The nitrogen gas has an advantage in that it induces no oxidation of the solder material and/or the land formed in the board and can further improve a wettability of the solder material.
As the mechanical shutter, a shutter which is made of a heat resistant material such as a stainless steel, a rubber or the like and which is mechanically operable to open and close can be used. Such a shutter can be operated such that the shutter in a closed condition will open when the board is conveyed and approaches to the closed shutter and the shutter closes again after the board is passed through the open shutter.
In yet another aspect of the present invention, there is provided a flow soldering process for mounting an electronic component onto a board by means of a solder material characterized in that, in a solder material supplying step for supplying the solder material in its molten state to the board which is provided with the electronic component on its upper surface by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board, a gas having a high temperature, preferably a temperature of 200 to 400xc2x0 C. and more preferably of 220 to 280xc2x0 C., is blown toward the upper surface of the board when the board is on the primary wave.
According to this process of the present invention, since the gas having the high temperature is blown toward the upper surface of the board when the board locates on the primary wave, the temperature decrease of the solder material is suppressed upon rising of the solder material supplied to the board. In a case, since the solder material is heated uniformly, it is possible to assure the wettability of the solder material sufficient to rise along the through hole formed through the board. Thus, the occurrence ratio of the xe2x80x9cinsufficient risingxe2x80x9d, the xe2x80x9cbridgexe2x80x9d and so on can be reduced effectively. The phrase xe2x80x9con the primary wavexe2x80x9d in the present specification means on a zone where the board contacts with the primary wave with respect to a flow direction of the primary wave toward the board and the zone may further include an area shifted upstream or downstream in the conveyance direction with respect to a cross section which includes the conveyance direction of the board (for example, on the secondary wave).
The gas described above may be blown toward the upper surface of the bard at any appropriate angle, for example from right above or obliquely above with respect to the board. In a preferred embodiment, the gas is blown toward it at an angle of xe2x88x9260 to +60 degrees with respect to a direction right to the upper surface of the board in a cross section containing the conveyance direction of the board. In such a case, a protrusion formed with the solder material which rises through the through hole and protrudes from the upper surface of the board can be flattened out over the upper surface of the board (preferably on a land) by a pressure of the blown gas. As a result, the solder material is likely to spread over the upper surface of the board.
It is noted that a value of the xe2x80x9canglexe2x80x9d in the specification is based on a direction which is upwardly perpendicular to the upper surface of the board in the cross section containing the conveyance direction for conveying the board (that is, such upwardly perpendicular direction defines an angle of zero degree), and the angle value is expressed with xe2x80x9c+xe2x80x9d sign when the angle is inclined toward upstream in the conveyance direction of the board and expressed with xe2x80x9cxe2x88x92xe2x80x9d sign when the angle is inclined toward downstream in the conveyance direction of the board with respect to the based direction.
Though air, nitrogen gas or the like can be used as the gas blown toward the board, nitrogen gas is preferable. Nitrogen gas has an advantage in that it induces no oxidation of the solder material and/or the land formed on the board and can further improve the wettability of the solder material. Additionally, it is preferable to use a gas which has been heated prior to being blown toward the board, though normal air (i.e. having a normal temperature) can also be used. In the case in which the air having a normal temperature is used, since such air is blown toward the board while involving the atmosphere gas around the board for heating, the gas having a substantially higher temperature is blown toward the board.
In a preferred embodiment, a sensor detects the presence of the board, and the blow of the gas is controlled depending on a detected result of the sensor so as to blow the gas when the board locates on the primary wave. In such embodiment, for example, when a plurality of the boards are conveyed intermittently, it is possible to reduce an amount of the gas blown toward the board and thereby to reduce power needed to blow the gas.
In another preferred embodiment of the present invention, there is provided a flow soldering apparatus for mounting an electronic component onto a board by means of a solder material, which apparatus includes: a solder material supplying unit for supplying the solder material in its molten state to the board, which is provided with an electronic component on its upper surface, by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board; and a blowing means (or device) for blowing a gas, preferably nitrogen gas having a high temperature, preferably 200 to 400xc2x0 C. and more preferably 220 to 280xc2x0 C. toward the upper surface of the board when the board locates on the primary wave. In a preferred embodiment, the blowing means blows the gas toward the upper surface of the board at an angle of xe2x88x9260 to +60 degrees, preferably 0 to +60 degrees, with respect to a direction right to the upper surface of the board in a cross section containing the conveyance direction of the board. The apparatus also includes: a sensor for detecting the presence of the board; and a controller for the blowing device to blow the gas when the board locates on the primary wave.
In other aspect of the present invention, there is provided a flow soldering process for mounting an electronic component onto a board by means of a solder material characterized in that in a solder material supplying step for supplying the solder material in its molten state to the board, which is provided with the electronic component on the upper surface, by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board, and that the primary wave and the secondary wave contact with the board while a distance xe2x80x9cd2xe2x80x9d between the primary wave and the secondary wave is not larger than 60 mm and preferably about 30 to 50 mm and more preferably about 40 mm. The phrase xe2x80x9cdistance between the primary wave and the secondary wavexe2x80x9d in the specification means a distance along which the board is carried after the board in contact with the primary wave leaves the primary wave and before the board comes to contact with the secondary wave.
Conventionally, the distance xe2x80x9cd2xe2x80x9d between the primary wave and the secondary wave is generally about 80 to 150 mm as shown in FIG. 17. On the other hand, since the primary wave and the secondary wave are set closer to the each other at a distance of 60 mm or less as in the present invention, the temperature decrease during the period after the board leaves the primary wave and before the board comes to contact with the secondary wave can be effectively reduced. Therefore, it can be effectively suppressed that the solder material supplied in the form of the primary wave to the board and adhered thereto in the molten state solidifies before a fresh solder material is supplied to the board in the form of the secondary wave. As a result, it is possible to effectively reduce the occurrence ratios of the xe2x80x9cinsufficient risingxe2x80x9d, the xe2x80x9cbridgexe2x80x9d or the like when the lead-free solder material is used. Further, it is also possible to reduce an amount of heat energy required to melt the solidified solder material once again by the secondary wave.
It is also possible to reduce the temperature decrease of the board during the period after leaving the primary wave and before contacting with the secondary wave to not larger than 50xc2x0 C. and preferably not larger than 30xc2x0 C., for example, by blowing the gas having the high temperature toward the board by reducing the heat dissipation of the atmosphere gas in the space locating above the solder bath so as to keep the temperature of the gas, and/or by preheating the board more effectively in the preheating step as described above, in addition to by decreasing the distance between the primary wave and the secondary wave.
In a preferred embodiment of the process of the present invention as described above, dross which stays between the primary wave and the secondary wave is mechanically discharged as a dross containing material (i.e. as a mixture of the dross and the solder material) between the primary wave and the secondary wave. In a more preferred embodiment, a vegetable oil containing material is added to the dross containing material which is discharged from between the primary wave and the secondary wave so as to separate the solder material at least partially from the dross containing material.
Generally, the dross which is an oxide produced through oxidation of the solder material floats on the surface of the molten solder material. Usually, the dross is periodically removed in the form of the dross containing material which contains the dross and the solder material since the dross causes quality degradation of a soldering part (fillet) and insufficient soldering. In the case of using the lead-free solder material, such dross is produced in an amount larger than that in the case of using the Snxe2x80x94Pb based solder material. When as in the present invention, the primary wave and the secondary wave are located closer to each other than in the conventional apparatus, the dross is likely to accumulate between the primary wave and the secondary wave and may occasionally climb up the surface of the wave countercurrently from between the primary wave and the secondary wave toward the top of the wave and adhere to the board. It is concerned that this may badly influence soldering. Thus, when the primary wave and the secondary wave are located closer to each other than the conventional apparatus according to the present invention, it is preferable to mechanically discharge the dross which stays between the primary wave and the secondary wave from between the primary wave and the secondary wave as the dross containing material. Such mechanical (or forced) discharge may be conducted successively while the flow soldering process is conducted, or intermittently at an interval between the flow soldering process and a next flow soldering process.
Though it is desirable to isolate the dross alone, the dross is generally removed in the form of the dross containing material which is a mixture of the dross and the solder material as described above, and as a result, the solder material as a useful component is wasted together with the dross. It has been known that the solder material can be recovered by adding the vegetable oil to the dross containing material to separate and recover the solder material at least partially from the dross containing material for the purpose of reducing a loss as the wasted solder material. As to a material containing the vegetable oil as a separating agent which can separate the solder material from the dross containing material, for example, Japanese Patent Kokai Publication Nos. H11-245030 and 2000-190073 describe using any one of saccharides, cereal grains or flours, bean flours, seed grains or flours, soybean-cake flours, and peanut hull flours, a combination thereof and the like. It is preferable also in the present invention to separate the solder material from the dross containing material at least partially by adding such separating agent to the dross containing material, and thereby to recover the useful solder material. It is noted that the contents of those two publications are incorporated herein by the reference thereto in their entireties.
In other aspect of the present invention, there is provided a flow soldering apparatus for mounting an electronic component onto a board by means of a solder material, characterized in that the apparatus includes a solder material supplying unit for supplying the solder material in its molten state to the board, which is provided with the electronic component on its upper surface, by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board, and that a distance between the primary wave and the secondary wave is not larger than 60 mm. The apparatus of the present invention preferably includes a discharging means (or device) for mechanically discharging dross which exists between the primary wave and the secondary wave as a dross containing material from a position between the primary wave and the secondary wave. More preferably, the apparatus further includes means (or unit or device) for adding a material which contains a vegetable oil to the dross containing material which is discharged from between the primary wave and the secondary wave so as to separate the solder material at least partially from the dross containing material.
Additionally, the present inventors have made extensive studies and found a temperature profile which is suitable to conduct the flow soldering using the lead-free solder material. According to the temperature profile obtained by us, the board which has been heated (or preheated) to 120xc2x0 C.xc2x130xc2x0 C. (i.e. 90 to 150xc2x0 C.) of the temperature of the board (more specifically, the temperature of a land surface located on a lower surface of the board) is contacted with the primary wave at first. Next, the temperature of the board is maintained at not less than 200xc2x0 C. during a period from leaving the primary wave of the board to contacting with the secondary wave of the board. Then, the board is cooled such that the temperature of the board is 150xc2x0 C.xc2x130xc2x0 C. (i.e. 120 to 180xc2x0 C.) at a point in time which is xe2x80x9c10 secondsxe2x80x9d later from a point in time at which the board leaves the secondary wave.
Such temperature profile can be established by any appropriate manner. The temperature ranges of the board in respective steps as described above can be realized by a manner for example as follows. The temperature of the board to be contacted with the primary wave can be made in the range of 120xc2x0 C.xc2x130xc2x0 C. by controlling the temperature of the preheater and/or by increasing the efficiency of preheating compared with that in the conventional case. The temperature of the board during the period from leaving the primary wave to beginning to contact with the secondary wave can be maintained not less than 200xc2x0 C. by setting a distance between the primary wave and the secondary wave smaller than in the conventional case, for example by setting the distance at about 60 mm or less. The temperature of the board after the board leaves the secondary wave is lowered by positively cooling the board by means of any appropriate cooling means (or device) such as a nozzle, an atomizer or the like which contacts a gas, a liquid or a mixture thereof with the board so as to cool the board. Thus, the temperature of the board can be 150xc2x0 C.xc2x130xc2x0 C. at a point in time which is 10 seconds later from the point in time at which the board leaves the secondary wave.
By keeping and controlling the temperature profile of the board so as to satisfying those requirements as described above in the flow soldering process, it is possible to effectively reduce the occurrence ratios of the xe2x80x9cinsufficient risingxe2x80x9d (or the generation of the xe2x80x9cred eyexe2x80x9d), the generation of the xe2x80x9cbridgexe2x80x9d, and the so-called xe2x80x9clift-offxe2x80x9d (that is, a phenomenon in which an edge of a fillet is lifted off a land portion which fillet is located on an upper and/or lower surface of the board and contacted with the fillet). This will be described later on more particularly.
The temperature profile described above is appropriate to conduct the flow soldering while selecting a conveyance speed of the board of, for example, about 1 to 2 m/min. (or about 1.6 to 3.3 cm/sec.). When the board is conveyed at a speed in such range, a period from leaving the primary wave of the board to contacting with the secondary wave of the board can be, for example, 3 to 5 seconds. When the conveyance speed of the board is out of such range, it can be readily understood by those skilled in the art that the point in time which is xe2x80x9c10 secondsxe2x80x9d later from the point in time at which the board leaves the secondary wave may be shifted appropriately depending on the conveyance speed.
The flow soldering processes and the apparatuses for the processes of the present invention are described above which are improved with various approaches. One of features of those flow soldering processes and the apparatuses of the present invention can be effective when it is used solely, but two or more features are preferably used in combination. These features can be selected in any combination.
Any of these flow soldering processes and apparatuses of the present invention is suitable for a case which uses a lead-free solder material such as an Snxe2x80x94Cu based material, an Snxe2x80x94Agxe2x80x94Cu based material, an Snxe2x80x94Ag based material, an Snxe2x80x94Agxe2x80x94Bi based material, an Snxe2x80x94Agxe2x80x94Bixe2x80x94Cu based material and the like as the solder material. However, the present invention is not limited to such, and a lead-containing solder material such as an Snxe2x80x94Pb based material can also be used.
As the board applicable to the present invention, it is possible to use, for example, a substrate of a paper phenol based material, a glass-epoxy based material, a polyimide film based material, a ceramic based material or other material. On the other hand, the electronic component which is connected (or soldered) to the board can be a through hole insertion component (e.g. a semiconductor, a capacitor, a resistor, a coil, a connector and so on) and/or a surface mount component located on a back surface of the board (e.g. a semiconductor, a capacitor, a resistor, a coil and so on). However, these are merely mentioned for a exemplary purpose, and should not be interpreted as any limitation of the present invention.
The flow soldering process of the present invention is preferably includes a flux applying step using a flux applying means (or unit or device), and the flow soldering apparatus of the present invention preferably includes the flux applying means. As the flux applying means, it is possible to use any one alone or in combination of a foaming mode flux applying means for contacting foamed flux with the board (e.g. a foam fluxer) and a spraying mode flux applying means for spraying atomized flux toward the board (e.g. a spray fluxer). For instance, the flux can be applied onto the board by means of the spraying mode means and thereafter by the foaming mode means or vice versa. The flux applying means can be incorporated to integrally constitute the flow soldering apparatus or separately located from the flow soldering apparatus.
Though the flow soldering processes and the apparatuses according to the present invention have been particularly described in the above, the present invention generally includes Modes 1 to 39 as follows:
(Mode 1)
A flow soldering process for mounting an electronic component onto a board by means of a solder material comprising:
a preheating step for previously heating the board by using a preheater locating under the board and a heating cover extending over (or covering the above of) the board, the board being provided with the electronic component and conveyed; and
a solder material supplying step for supplying the solder material in its molten state to the board by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board.
(Mode 2)
A flow soldering process for mounting an electronic component onto a board by means of a solder material comprising:
a preheating step for previously heating the board by using a preheater locating under the board, the board being provided with the electronic component and conveyed; and
a solder material supplying step for supplying the solder material in its molten state to the board by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board which has been previously heated, wherein a temperature decrease of the board during a period after being previously heated in the preheating step before contacting with the primary wave is not larger than 3xc2x0 C.
(Mode 3)
A flow soldering process for mounting an electronic component onto a board by means of a solder material comprising:
a preheating step for previously heating the board by using a preheater locating under the board, the board being provided with the electronic component and conveyed; and
a solder material supplying step for supplying the solder material in its molten state to the board by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board while an atmosphere gas above the solder material in the molten state is thermally isolated from a gas which is downstream of the atmosphere gas in a direction of conveyance of the board and has a temperature lower than that of the atmosphere gas.
(Mode 4)
The process according to Mode 3, wherein a heating cover extending over the board is further used for previously heating the board in the preheating step.
(Mode 5)
The process according to any one of Modes 1, 3 and 4, wherein the solder material supplying step comprises having a temperature decrease of the board during a period after being previously heated in the preheating step before contacting with the primary wave not larger than 3xc2x0 C.
(Mode 6)
The process according to any one of Modes 1 to 5, wherein a temperature decrease of the board during a period after leaving the primary wave of the board before contacting with the secondary wave of the board is not larger than 50xc2x0 C.
(Mode 7)
The process according to any one of Modes 1 to 6, wherein the solder material is a lead-free solder material selected from the group consisting of an Snxe2x80x94Cu based material, an Snxe2x80x94Agxe2x80x94Cu based material, an Snxe2x80x94Ag based material, an Snxe2x80x94Agxe2x80x94Bi based material and an Snxe2x80x94Agxe2x80x94Bixe2x80x94Cu based material.
(Mode 8)
A flow soldering apparatus for mounting an electronic component onto a board by means of a solder material comprising:
a preheater locating under the board which is provided with the electronic component and conveyed;
a heating cover locating above the preheater so as to extend over (or cover the above of) the board; and
a solder material supplying means for supplying the solder material in its molten state to the board by contacting the solder material as a primary wave and secondary wave successively with a lower surface of the board, the means locating downstream of the preheater in a direction of conveyance of the board.
(Mode 9)
A flow soldering apparatus for mounting an electronic component onto a board by means of a solder material comprising:
a preheater locating under the board which is provided with the electronic component and conveyed; and
a solder material supplying means for supplying to the board the solder material in its molten state contained in a solder bath by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board, the means locating downstream of the preheater in a direction of conveyance of the board and being constructed to set a width of a gap between the preheater and the solder bath within 20 to 60 mm.
(Mode 10)
A flow soldering apparatus for mounting an electronic component onto a board by means of a solder material comprising:
a preheater locating under the board which is provided with the electronic component and conveyed;
a solder material supplying means for supplying the solder material in its molten state to the board by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board, the means locating downstream of the preheater in a direction of conveyance of the board; and
an isolation means for thermally isolating an atmosphere gas above the solder material supplying means from a gas which is downstream of the atmosphere gas in a direction of conveyance of the board and has a temperature lower than that of the atmosphere gas.
(Mode 11)
The apparatus according to Mode 10 wherein the isolation means is an air curtain or a mechanical shutter.
(Mode 12)
The apparatus according to Mode 10 or 11, further comprising a heating cover locating above the preheater to extend over (or cover the above of) the board.
(Mode 13)
The apparatus according to Mode 8 or 12, wherein the heating cover extends over also the solder material supplying means so as to cover the above of the board.
(Mode 14)
The apparatus according to any one of Modes 8, 12 and 13, wherein the heating cover is composed of plural sections and each of the sections is controlled for heating with the heating cover.
(Mode 15)
The apparatus according to any one of Modes 8 and 12 to 14, further comprising a forced convection generating means for forcedly convecting an atmosphere gas in a space between the heating cover and the preheater.
(Mode 16)
The apparatus according to Mode 15, wherein the forced convection generating means is a fan or a gas blowing means.
(Mode 17)
The apparatus according to any one of Modes 8 and 10 to 16, wherein the solder material supplying means comprises a solder bath which contains the solder material in the molten state, and wherein a width of a gap between the preheater and the solder bath is within 20 to 60 mm.
(Mode 18)
The apparatus according to Mode 9 or 17, further comprising a closing means for closing the gap between the preheater and the solder bath so as to prevent a gas stream from passing through the gap.
(Mode 19)
The apparatus according to any one of Modes 8 to 18, wherein the solder material supplying means is constructed to set a distance between the primary wave and the secondary wave which contacts with the board not larger than 60 mm.
(Mode 20)
The apparatus according to any one of Modes 8 to 19, wherein the solder material is a lead-free solder material selected from the group consisting of an Snxe2x80x94Cu based material, an Snxe2x80x94Agxe2x80x94Cu based material, an Snxe2x80x94Ag based material, an Snxe2x80x94Agxe2x80x94Bi based material and an Snxe2x80x94Agxe2x80x94Bixe2x80x94Cu based material.
(Mode 21)
A flow soldering process for mounting an electronic component onto a board by means of a solder material characterized in that in a solder material supplying step for supplying the solder material in its molten state to the board by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board, the board being provided with the electronic component on the upper surface, and that a gas having a high temperature is blown toward the upper surface of the board when the board is on a primary wave.
(Mode 22)
The process according to Mode 21, wherein the gas has a temperature of 200 to 400xc2x0 C.
(Mode 23)
The process according to Mode 21 or 22, wherein the gas is blown toward the upper surface of the board at an angle of xe2x88x9260 to +60 degrees from a direction right to the upper surface of the board in a cross section which contains a direction of conveyance of the board.
(Mode 24)
The process according to any one of Modes 21 to 23, wherein the gas is nitrogen gas.
(Mode 25)
The process according to any one of Modes 21 to 24, which comprises detecting the presence of the board by a sensor and controlling the blow of the gas depending on a detected result of the sensor so as to blow the gas when the board is located on the primary wave.
(Mode 26)
A flow soldering apparatus for mounting an electronic component onto a board by means of a solder material comprising:
a solder material supplying means for supplying the solder material in its molten state to the board by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board, the board being provided with the electronic component on its upper surface; and
a blowing means for blowing a gas having a high temperature toward the upper surface of the board when the board is located on the primary wave.
(Mode 27)
The apparatus according to Mode 26, wherein the gas has a temperature of 200 to 400xc2x0 C.
(Mode 28)
The apparatus according to Mode 26 or 27, wherein the blowing means blows the gas toward the upper surface of the board at an angle of xe2x88x9260 to +60 degrees from a direction right to the upper surface of the board in a cross section which contains a direction of conveyance of the board.
(Mode 29)
The apparatus according to any one of Modes 26 to 28, wherein the gas is nitrogen gas.
(Mode 30)
The apparatus according to any one of Modes 26 to 29, further comprising:
a sensor for detecting the presence of the board; and
a controller for controlling the blowing means to blow the gas when the board is located on the primary wave.
(Mode 31)
A flow soldering process for mounting an electronic component onto a board by means of a solder material characterized in that in a solder material supplying step for supplying the solder material in its molten state to the board by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board, the board being provided with the electronic component on the upper surface, and that the primary wave and the secondary wave contact with the board so as to set a distance between the primary wave and the secondary wave not larger than 60 mm.
(Mode 32)
The process according to Mode 31, wherein dross which exists between the primary wave and the secondary wave is mechanically discharged as a dross containing material from between the primary wave and the secondary wave.
(Mode 33)
The process according to Mode 32, wherein a vegetable oil containing material is added to the dross containing material which is discharged from between the primary wave and the secondary wave to at least partially separate the solder material from the dross containing material.
(Mode 34)
A flow soldering apparatus for mounting an electronic component onto a board by means of a solder material comprising a solder material supplying means for supplying the solder material in its molten state to the board by contacting the solder material as a primary wave and a secondary wave successively with a lower surface of the board, the board being provided with the electronic component on its upper surface, characterized in that a distance between the primary wave and the secondary wave is not larger than 60 mm.
(Mode 35)
The apparatus according to Mode 34, comprising a discharging means for mechanically discharging dross which exists between the primary wave and the secondary wave as a dross containing material from between the primary wave and the secondary wave.
(Mode 36)
The apparatus according to Mode 35, further comprising a means for adding a vegetable oil containing material to the dross containing material which is discharged from between the primary wave and the secondary wave to at least partially separate the solder material from the dross containing material.
(Mode 37)
A flow soldering process comprising contacting a solder material as a primary wave and a secondary wave successively with a lower surface of a board which is provided with an electronic component on its upper surface, characterized by:
contacting the board with the primary wave, wherein the board has been previously heated so as to have a temperature of the board of 90 to 150xc2x0 C.;
maintaining the temperature of the board not less than 200xc2x0 C. during a period after leaving the primary wave of the board before contacting with the secondary wave of the board; and
cooling the board such that the temperature of the board is 120 to 180xc2x0 C. at a point in time which is 10 seconds later from a point in time at which the board leaves the secondary wave.
(Mode 38)
The process according to any one of Modes 21 to 25, 31 to 33 and 37, wherein the solder material is a lead-free solder material selected from the group consisting of an Snxe2x80x94Cu based material, an Snxe2x80x94Agxe2x80x94Cu based material, an Snxe2x80x94Ag based material, an Snxe2x80x94Agxe2x80x94Bi based material and an Snxe2x80x94Agxe2x80x94Bixe2x80x94Cu based material.
(Mode 39)
The apparatus according to any one of Modes 26 to 30 and 34 to 36, wherein the solder material is a lead-free solder material selected from the group consisting of an Snxe2x80x94Cu based material, an Snxe2x80x94Agxe2x80x94Cu based material, an Snxe2x80x94Ag based material, an Snxe2x80x94Agxe2x80x94Bi based material and an Snxe2x80x94Agxe2x80x94Bixe2x80x94Cu based material.